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Show N 0 ~ 0 a .2 '"0 2 u QJ L-L- 0 u E a. a. c .2 0 L-C QJ U C 0 u Z u.. > I- ~ z 700 600 SOO 400 300 200 100 0 - 14 - I • / / / / furnace no.1 cool reburning / +--=----~------------~~r---------~------cf_-----+~ / 0 0 • /0 IPFR coal gas • • 0 NOx • 0 TYFN • 0 08 0.9 1.0 1.1 effective rebum zcne stoichiometry Figure 12: NOx and TVFN concentrations in the reburn zone experiments TVFN was relatively insensitive to ARB, and remained constant at approximately 300 ppm for ARB less than 0.9, Figure 12. The TVFN concentration was also insensitive to the reburn zone residence time. For residence time greater than 0.3 s, the TVFN concentration remained constant with a redistribution of N-species. At ARB less than 0.9 and residence time greater than 0.3 s, NH3 was the most abundant N-species. Natural gas was a better fuel for NOx reduction than the coal. At a primary stoichiometry of 1.05 and 13% reburn fuel fraction (ARB - 0.92), the NOx concentration was reduced from 1000 ppm at the inlet to less than 60 ppm after 0.3 s. For similar conditions, the NOx concentration for coal reburning in the IPFR was calculated as 420 ppm. Therefore, the absence of fuel-N and the added volatility of the natural gas improved NOx reduction. The TVFN concentration with natural gas reburning was 260 ppm (or 26% of the inlet NOx) after 0.3 s for ARB equal to 0.97. As found with the coal reburning, NH3 was the predominant fmal species. The TVFN concentration was within the range of NOx emissions measured in Test M8 for natural gas reburning. 5.0 Discussion The correlation of NOx emissions measured in the furnace experiments as a function of Aeff is also shown in Figure 12. These NOx emissions were much higher than measured in the reburn zone experiments, particularly at Aeff less than 0.9. However, the NOx emissions from the furnace experiments were similar to the TVFN from teh reburn zone experiments over the entire range in Aeff. The lack of agreement in NOx reductions between the two experiments may have been due to the large differences in mixing rates of the reburn fuel and primary combustion products. The extent that the mixing differed in the two experiments was estimated using a technique developed from computational modelling [11]. The mixing rates were calculated for each term of the transport equation for the time averaged species |
